Plastic cards bearing a magnetisable stripe are known. Information in the form of differentially magnetised zones of the magnetic stripe can be written using a magnetic write head and can be read by a read head provided there is relative movement between the card and the head.
Where the card is one which signifies pre-payment of a service or facility such as electricity or gas, it is important that the card be cancelled after the card has been entered into a card reader associated with the service or facility for which pre-payment has been made.
A card reader will normally include a reading head and hitherto, adjacent the reading head has been located an erase head comprising an electro-magnet, current for which has been derived from an appropriate control circuit which is triggered to provide the erasure current as soon as the information derived from the read head has been indicated as satisfactory by logic circuitry associated with the reading head. However the current requirements for an erase head and the time required for the current to flow make quite significant demands on the power supply for the unit and in addition, since the current for the erase head is controlled by a processor, the latter cannot be turned off until after the card has been detected as having been removed from the card reader. Again this makes considerable demands on the power supply requirements for the card reader.
It is an object of the present invention to provide an alternative erasure device for erasing magnetically stored information on the card after it has been read.